Calibrated airflow sensor facilitating monitoring of electronic system cooling

ABSTRACT

A calibrated airflow sensor and monitoring method are provided. The monitoring method which includes: providing an airflow sensor positioned within an electronic system to be at least partially air-cooled, the airflow sensor including at least one temperature sensor and a heater associated with one temperature sensor of the at least one temperature sensor; calibrating, with the airflow sensor positioned within the electronic system, a duty cycle for use in powering the heater associated with the one temperature sensor; and providing a controller configured to use the calibrated duty cycle in powering the heater of the temperature sensor during airflow monitoring of the electronic system, and to obtain a hot temperature (T hot ) reading from the one temperature sensor having the associated heater, and to determine, based at least in part on the hot temperature (T hot ) reading, whether to issue an airflow warning.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH

This invention was made with government support under Contract No.HR0011-07-9-0002, awarded by the Defense Advanced Research ProjectsAgency (DARPA) of the U.S. Government. Accordingly, the U.S. Governmenthas certain rights in the invention.

BACKGROUND

The power dissipation of integrated circuit chips, and the modulescontaining the chips, continues to increase in order to achieveincreases in processor performance. This trend poses a cooling challengeat both module and system levels. Increased airflow rates are oftenneeded to effectively cool high power modules and to limit thetemperature of the air that is exhausted into the computer center.

In many large server applications, processors along with theirassociated electronics (e.g., memory, disk drives, power supplies, etc.)are packaged in removable drawer configurations stacked within a rack orframe. In other cases, the electronics may be in fixed locations withinthe rack or frame. Typically, the components are cooled by air moving inparallel airflow paths, usually front-to-back, impelled by one or moreair moving devices (e.g., fans or blowers). In some cases it may bepossible to handle increased power dissipation within a single drawer byproviding greater airflow, through the use of a more powerful air movingdevice or by increasing the rotational speed (i.e., RPMs) of an existingair moving device. However, this approach may become problematic at therack level in the context of a computer installation (i.e., datacenter).

The sensible heat load carried by the air exiting the rack may stressthe capability of the room air-conditioning to effectively handle theload. This is especially true for large installations with “serverfarms” or large banks of computer racks located close together. In suchinstallations, supplemental liquid cooling (e.g., water or refrigerantcooling) is an attractive technology to manage the higher heat fluxes.The liquid absorbs the heat dissipated by the components/modules in anefficient manner. Typically, the heat is ultimately transferred from theliquid to an outside environment, whether air or liquid cooled.

BRIEF SUMMARY

In one aspect, provided herein is a method which includes: providing anairflow sensor positioned within an electronic system to be cooled, theairflow sensor comprising at least one temperature sensor and a heaterassociated with one temperature sensor of the at least one temperaturesensor; calibrating, with the airflow sensor positioned within theelectronic system, a duty cycle for use in powering the heaterassociated with the one temperature sensor of the at least onetemperature sensor; and providing a controller, the controller beingconfigured to use the calibrated duty cycle in powering the heaterassociated with the one temperature sensor of the at least onetemperature sensor during airflow monitoring of the electronic system,and to obtain a hot temperature (T_(hot)) reading from the temperaturesensor having the associated heater powered using the calibrated dutycycle, and to determine, based at least in part on the hot temperature(T_(hot)) reading, whether to issue a warning.

In another aspect, an airflow monitoring method is provided whichincludes: employing an airflow sensor positioned within an electronicsystem to be cooled, the airflow sensor comprising at least onetemperature sensor and a heater associated with one temperature sensorof the at least one temperature sensor. The employing includes:obtaining a calibrated duty cycle for use in powering the heaterassociated with the one temperature sensor of the at least onetemperature sensor; using the calibrated duty cycle in powering theheater associated with the one temperature sensor of the at least onetemperature sensor; obtaining a hot temperature (T_(hot)) reading fromthe one temperature sensor having the associated heater being poweredusing the calibrated duty cycle; and determining, based at least in parton the hot temperature (T_(hot)) reading, whether to issue a warning.

In a further aspect, a monitored electronic system is provided whichincludes an electronic system at least partially air-cooled, and amonitoring device for monitoring air-cooling of the electronic system.The monitoring device includes an airflow sensor, non-volatile memory,and a controller. The airflow sensor is positioned within the electronicsystem, and includes at least one temperature sensor and a heaterassociated with one temperature sensor of the at least one temperaturesensor. The non-volatile memory contains a calibrated duty cycle for usein powering the heater associated with the one temperature sensor, withthe calibrated duty cycle having been obtained with the airflow sensorpositioned within the electronic system. The controller is configured touse the calibrated duty cycle in powering the heater associated with theone temperature sensor of the at least one temperature sensor duringairflow monitoring of the electronic system, and to obtain a hottemperature (T_(hot)) reading from the one temperature sensor having theassociated heater powered using the calibrated duty cycle, and todetermine, based at least in part on the hot temperature (T_(hot))reading, whether to issue a warning.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more aspects of the present invention are particularly pointedout and distinctly claimed as examples in the claims at the conclusionof the specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one embodiment of a conventional raised floor layout ofan air-cooled data center;

FIG. 2 is a cross-sectional elevational view of one embodiment of anelectronics rack comprising multiple electronic systems, one or more ofwhich may be monitored employing a calibrated airflow sensor, inaccordance with one or more aspects of the present invention;

FIG. 3 is a schematic of one embodiment of an electronic system with oneor more airflow sensors, and shown disposed within a calibrationenvironment for undergoing calibration of airflow measurement sensing,in accordance with one or more aspects of the present invention;

FIG. 4 is a schematic of one embodiment of an airflow sensor to beemployed as a monitoring device, in accordance with one or more aspectsof the present invention;

FIG. 5 graphically depicts sensor temperature versus heater time for anairflow sensor being powered using a set duty cycle, the duty cycledefining multiple sequential micro-cycles of powering the heater, inaccordance with one or more aspects of the present invention;

FIG. 6 depicts one embodiment of a process for monitoring airflowcooling of an electronic system, in accordance with one or more aspectsof the present invention;

FIGS. 7A & 7B depict one embodiment of a process for calibrating anairflow sensor to facilitate monitoring airflow cooling, in accordancewith one or more aspects of the present invention; and

FIG. 8 depicts one embodiment of a computer program product or articleof manufacture incorporating one or more aspects of the presentinvention.

DETAILED DESCRIPTION

As used herein, the terms “electronics rack”, “rack-mounted electronicequipment”, and “rack unit” are used interchangeably, and unlessotherwise specified include any housing, frame, rack, compartment, bladeserver system, etc., having one or more heat generating components of acomputer system or electronics system, and may be, for example, astand-alone computer processor having high, mid or low end processingcapability. In one embodiment, an electronics rack may comprise one ormore electronic systems, each having one or more heat generatingcomponents disposed therein requiring cooling. “Electronic system”refers to any housing, blade, book, drawer, node, compartment, etc.,having one or more heat generating electronic components disposedtherein. Each electronic system of an electronics rack may be movable orfixed relative to an electronics rack, with the nodes of an IBM® Power®775™ Supercomputer being one example of electronic systems of anelectronics rack to be cooled. (IBM®, Power®, Power 775™ are trademarksof International Business Machines Corporation, Armonk, N.Y., USA.)Further, “data center” refers to a computer installation containing oneor more electronics racks to be cooled. As a specific example, a datacenter may include one or more rows of rack-mounted computing units.

Reference is made below to the drawings, which are not drawn to scalefor ease of understanding, wherein the same reference numbers usedthroughout different figures designate the same or similar components.

FIG. 1 depicts a raised floor layout of an air cooled data center 100typical in the prior art, wherein multiple electronics racks 110 aredisposed in one or more rows. A data center such as depicted in FIG. 1may house several hundred, or even several thousand microprocessors. Inthe arrangement illustrated, chilled air enters the computer room viaperforated floor tiles 160 from a supply air plenum 145 defined betweenthe raised floor 140 and a base or sub-floor 165 of the room. Cooled airis taken in through louvered or screened doors at air inlet sides 120 ofthe electronics racks and expelled through the backs or air outlet sides130 of the electronics racks. Each electronics rack 110 may have one ormore air-moving devices (e.g., fan or blower) to provide forcedinlet-to-outlet airflow to cool the electronic components within theelectronic system(s) of the rack. The supply air plenum 145 providesconditioned and cooled air to the air-inlet sides of the electronicsracks via perforated floor tiles 160 disposed in a “cold” aisle of thecomputer installation. The conditioned and cooled air is supplied toplenum 145 by one or more air-conditioning units 150, also disposedwithin the data center 100. Room air is taken into each air-conditioningunit 150 near an upper portion thereof. This room air may comprise (inpart) exhausted air from the “hot” aisles of the computer installationdefined, for example, by opposing air outlet sides 130 of electronicsracks 110.

FIG. 2 is an elevational representation of one embodiment of anelectronics rack 110, shown comprising a plurality of electronic systems201, which (in the embodiment illustrated), are a least partiallyair-cooled by cool air 202 ingressing via louvered air inlet door 120,and exhausting out louvered air outlet door 130 as hot air 203.Electronics rack 110 also includes one or more bulk power assemblies 204of the AC-to-DC power supply assembly. AC-to-DC power supply assemblymay further include, in one embodiment, a frame controller, which may beresident in the bulk power assembly 204 and/or in one or more electronicsystems 201. Each electronic system 201 includes, in one example, one ormore processors and associated memory. Also illustrated in FIG. 2 is oneor more input/output (I/O) drawer(s) 205, which may also include aswitch network. I/O drawer(s) 205 may include, for example, PCI cardslots and disk drivers for the electronics rack.

A three-phase AC source feeds power via an AC power supply line cord 206to bulk power assembly 204, which transforms the supplied AC power to anappropriate DC power level for output via distribution cable 207 to theplurality of electronic systems 201 and I/O drawer(s) 205. The number ofelectronic systems installed in the electronics rack is variable anddepends on customer requirements for a particular system. Further, theconfiguration of the bulk power assembly of the AC-to-DC power supplyassembly is variable and is determined, in one implementation, by thenumber of electronic systems installed in the electronics rack, or moreparticularly, by the power requirements of the common load of theelectronics rack being fed by the AC-to-DC power supply assembly.

FIG. 3 is a schematic of one embodiment of electronic system 201 of FIG.2, and illustrates one embodiment of an air-moving device 340 and anautomated controller 350 associated therewith, in accordance with anaspect of the present invention. As illustrated, electronic system 201may include one or more multi-chip modules (MCM) 310, which may beliquid-cooled, employing one or more liquid-cooled cold plates (notshown). Supporting electronics for multi-chip module 310 include one ormore memory modules 320, such as one or more DIMMs, and one or moresubsystem power supplies, such as the three distributed converterassembly (DCA) supplies 330 illustrated.

As shown in FIG. 3, air-moving device 340 includes an air-moving bladeassembly, typically driven by a motor 341 at a normal operatingrotational velocity. The rotational velocity of an air-moving devicewithin an electronics rack is conventionally set by the rackmanufacturer to account for a variety of anticipated ambienttemperature, altitude, heat load, configuration and motor variations,which taken together effect the safe, operating rotational velocity ofthe air-moving device.

The heat produced by the electronic components within the electronicsystem must be transported away to avoid damage to the components. Acontroller 350 is provided to monitor temperature within the electronicsystem and to, for example, dynamically adjust speed or rotation ofmotor 341 of air-moving device 340 via, for example, a control line 342between controller 350 and motor 341. Thermal sensing can beaccomplished via one or more temperature sensors 301 (such asthermistors) disposed, for example, within electronic system 201. Notein this regard, that although described herein with reference toelectronic system 201, the thermal sensing and calibration processespresented are equally applicable to monitoring airflow cooling of anyelectronic system, such as a bulk power assembly 204 (see FIG. 2) or I/Odrawer 205 (see FIG. 2) of an electronics rack, as well as any other atleast partially air-cooled electronic system.

As described herein, thermal sensing may be in the form of thermistors,thermocouples, RTDs, or temperature sensing diodes, etc. applied tovarious electronics within the electronic system to be cooled, and oneor more of the sensed temperatures are compared, in one example, to oneor more thresholds by a controller executing within or coupled to theelectronic system, to provide both a means to shut down the electronicsystem to prevent damage, as well as a feedback control signal toincrease cooling (for example, by increasing a fan speed). In an idealimplementation, all critical components within the electronic system orenclosure have thermal sensing and damage protection as described hereinassociated with them. However, certain components within the system maynot be configured for easy application of thermal sensing. Air coolingof such components is necessarily inferred by looking at temperatures inother locations within the electronic system/enclosure, or by sensingthe air flow through the electronic system/enclosure. In the example ofFIG. 3, airflow sensors 301 are disposed, for example, on a printedcircuit board 302 positioned within the electronic system 201 forsensing airflow 305 across electronic system 201. As explained furtherbelow, in one embodiment, airflow sensors 301 are initially calibratedwithin a calibration environment or system 300 comprising a controlledcalibration environment with a known ambient temperature and knownambient airflow 305 across the electronic system 201.

By way of example, airflow sensor 301 comprises, in one embodiment, atleast one temperature sensor, and at least one heater associated withone temperature sensor of the at least one temperature sensor. FIG. 4depicts one embodiment of such an airflow sensor 301, wherein a firsttemperative sensor 400 has associated therewith one or more heaters 402,and offset from temperature sensor 400 is a second temperature sensor401. Note that in alternate embodiments, multiple heaters could beassociated with first temperature sensor 400, for example, on eitherside of the sensor, or still further, a single temperature sensor couldbe employed in obtaining the hot temperature (T_(hot)) and ambienttemperature (T_(amb)) readings discussed herein.

As one example, heater 402 is a resistor, and in operation, currentflowing through the resistor dissipates heat, which raises thetemperature of temperature sensor 400 above the ambient airflow 403temperature read by second temperature sensor 401. The hot temperature(T_(hot)) of temperature sensor 400 above that of second temperaturesensor 401 is a function of the rate of airflow across the sensors 400,401 and heater 402. In one implementation, the ambient temperature(T_(amb)) is available through, for example, second temperature sensor401. In those cases where component density within the electronic systemor enclosure results in temperature sensors being placed within theenclosure where they could be affected by the total heat dissipationwithin the electronic system, it may be desirable to employ a singletemperature sensor in obtaining a high, hot level reading and a low,ambient reading.

Complications arise in monitoring airflow and cooling of an electronicsystem due to variabilities between the airflow sensors and theoperation of airflow sensors between systems. For example, there can bevariability in the power delivered to the heaters (e.g., resistors), thetolerance of the heaters themselves, the tolerance of the temperaturesensors (e.g., thermistors) and the associated temperature measurements,as well as variability from specific electronicsystem/enclosure-to-electronic system/enclosure. Disclosed hereintherefore, in one aspect, are approaches for calibrating an airflowsensor, and for measuring airflow within the electronic system using thecalibrated airflow sensor to facilitate monitoring cooling of theelectronic system and, for example, automated deactivation of theelectronic system based upon an identified cooling error.

Generally stated, disclosed herein is a method which includes providingan airflow sensor positioned within an electronic system to be cooled,wherein the airflow sensor includes at least one temperature sensor anda heater associated with one temperature sensor of the at least onetemperature sensor. A calibrated duty cycle is also provided forpowering the heater associated with the one temperature sensor, and acontroller is coupled to the airflow sensor for reading temperaturesfrom the airflow sensor. The controller employs the calibrated dutycycle in powering the heater associated with the one temperature sensor,and obtains a hot temperature (T_(hot)) reading from the one temperaturesensor having the associated heater powered using the calibrated dutycycle. The controller determines, based at least in part on the hottemperature (T_(hot)) reading, whether to issue an airflow warning, orwhether to take other action, such as increasing speed of an air-movingdevice, or deactivating the associated electronic system. A detailedembodiment for calibrating the duty cycle for the airflow sensorpositioned within the electronic system is also described. As noted, bycalibrating the duty cycle, greater confidence in the accuracy of themonitoring disclosed is obtained. In one embodiment, by comparing thehot temperature (T_(hot)) reading with an ambient temperature (T_(amb))reading, airflow rate through the electronic system can be inferred, andcompared to one or more threshold values which may be used, for example,to increase the RPMs of the one or more air-moving devices of theelectronic system, issue airflow warnings, and/or deactivate power tothe electronic system.

In the example of FIG. 4, the airflow sensor may comprise standard,surface-mount components on an electronics board, such as a printedcircuit board. Relevant characteristics of such a sensor include:

-   -   the printed circuit board under the temperature sensor(s) (e.g.,        thermistor(s)) may be damaged if the temperature of the heater        exceeds the board rating, so an upper limit to the heater        temperature restricts the sensitivity of the sensor;    -   the temperature sensor and associated analog-to-digital        converter components result in an approximately +/−4° C.        uncertainty in the temperature readings;    -   the transient response of the sensor is dominated by the printed        circuit board since the main path for heat to flow from the        heater (e.g., resistor) to the associated temperature sensor        (e.g., thermistor) is through the board;    -   the heat transfer from (for example) the thermistor(s),        resistor(s) and board to air is a function of airflow rate, such        that a higher airflow rate results in a smaller temperature        difference between the hot temperature (T_(hot)) reading and the        ambient air temperature (T_(amb));    -   even if 1% tolerance resistors are employed, there is        unit-to-unit variability in the power dissipated at a given duty        cycle;    -   variability in the resistor (or heater) source voltage results        in a variation in the power dissipation (Q=V²/R); and    -   calibration is desirable to achieve sensor performance in the        two critical temperatures, that is, the sensor must not indicate        low airflow when sufficient airflow is present (that is, no        false trips), and the sensor must indicate low airflow when the        enclosure is at risk of overheating.

FIG. 5 depicts one embodiment of a duty cycle which can be employed inpowering a heater associated with a temperature sensor of an airflowsensor, such as described above in connection with FIG. 4. In thisfigure, temperature sensed versus heater ON time is illustrated. Forpurposes of explanation, the duty cycle is assumed to be a small,micro-time scale, such as 1,005 milliseconds. Heater ON micro-timerefers to that portion of the duty cycle that the heater is powered, andheater OFF micro-time refers to that portion of the duty cycle that theheater is not powered. As one example, the duty cycle might comprise OFFfor 30% and ON for 70%, and in a 1,005 millisecond duty cycle, thismeans the heater is OFF for approximately 300 milliseconds, and ON forapproximately 700 milliseconds. By so controlling powering of theheater(s), the heat applied by the airflow sensor in the vicinity of theassociated temperature sensor can be accurately controlled, thusproviding better accuracy for the airflow sensing determinationsdescribed herein.

As noted, the difference between a hot temperature (T_(hot)) reading andan ambient temperature (T_(amb)) reading is proportional to the airflowacross the airflow sensor. Using Newton's law of cooling, and assumingthat the time scales are long enough to reach a steady statetemperature, and that the airflow rate is sufficiently high that theheat transfer coefficient is only a function of airflow rate andgeometry, heat dissipated from the heater(s) can be expressed as:

Q=hA(T _(hot) −T _(amb))

where Q is the heat dissipated from the heater, h is the heat transfercoefficient, A is the area being cooled, T_(hot) is the temperature ofthe cooled surface, and T_(amb) is the temperature of the ambient air.Since the readings are taken at two states, at two different heattransfer rates, then the temperature difference is inverselyproportional to the heat transfer coefficient, and therefore, also theair velocity. Thus, since the heat transfer coefficient is driven by theair velocity over the cooled surfaces, the temperature differencebetween the hot reading and the ambient reading can be used to inferairflow velocity.

In FIG. 5 the dashed line indicates a continuous reading of theassociated temperature sensor along the illustrated duty cycle.Described further below with reference to FIGS. 7A & 7B, is one methodfor calibrating a duty cycle of an airflow sensor comprising one or moreresistive heaters and one or more temperature sensors (i.e., measurementdevices), such as one or more thermistors. Additionally, disclosedherein is a monitoring approach using the airflow sensor with thecalibrated duty cycle, which compares obtained temperature readings toone or more thresholds and which automatically initiates action toprotect the electronic system from high temperature environments and/orlow airflow conditions.

FIG. 6 depicts one embodiment of a process for monitoring cooling of anelectronic system, in accordance with one or more aspects of the presentinvention. The process depicted in FIG. 6 employs one or more calibratedairflow sensors, such as described herein. Note that this processing ispresented by way of example only.

After powering ON the electronic system 600, a calibrated duty cycle nis obtained, for example, from non-volatile memory, and the temperaturereadings T_(hot) and T_(amb) are cleared by the controller 605.Processing waits a time interval t 610 for temperature within theelectronic system to stabilize after being powered on. The heater isactivated for a period of time, calculated by multiplying the duty cyclen by a predetermined micro-cycle time interval, such as a 1005millisecond interval 615.

A hot temperature (T_(hot)) reading is obtained 620, via one of thetemperature sensors, and compared against a set maximum board thresholdtemperature (T_(max,b)) 625. The maximum board threshold temperature(T_(max,b)) corresponds to a temperature above which the board (orsubstrate) upon which the heater (e.g., resistor(s)) resides would bedamaged, as read by the associated temperature sensor some distance away(see FIG. 4), and might be, by way of example, 95° C. If the hottemperature (T_(hot)) reading is above the maximum board thresholdtemperature (T_(max,b)) 625, then a critical board over temperatureexists, and processing issues an error message and deactivates theelectronic system 630.

Assuming that the hot temperature (T_(hot)) reading is below the maximumboard threshold temperature (T_(max,b)), then the heater is deactivatedfor a period of time corresponding to the OFF portion of the duty cycle635, and an ambient temperature (T_(amb)) reading 640 is obtained. Notethat in the embodiment of FIG. 4, the ambient temperature reading isascertained by a different temperature sensor (or thermistor) than thatemployed in obtaining the hot temperature (T_(hot)) reading. In analternate embodiment, they could be the same temperature sensors.

The difference between the hot and ambient temperature (T_(hot)−T_(amb))readings is then determined and compared against a low airflow criticallimit (T_(max,crit)) 645, which corresponds to an airflow across theairflow sensor which is at or below the minimum airflow required for thesystem to ensure such that no components will be damaged. When thetemperature difference (T_(hot)−T_(amb)) exceeds the low airflowcritical limit (T_(max,crit)), processing issues a critical airflowerror message, and deactivates the electronic system 650.

One of the constraints on the operation of the airflow sensor is thatthe temperature of the electronics board under the heater must not bedamaged by excessive temperature. For example, if the electronics boardunder the airflow sensor has an operating limit of 130° C.,corresponding to a 95° C. reading at the temperature sensor, then at thelowest valid airflow and hottest room temperature (corresponding to thehighest operational thermistor temperature), the ambient temperatureplus the acceptable temperature differential (ΔT_(spec)) must be, forexample, below 95° C. Since ΔT_(spec)=T_(hot)−T_(amb), if the productmust operate at a 50° C. room, then if the airflow is equal to theairflow warning limit (i.e., lowest valid airflow), the resulting sensortemperature difference should be 95° C.−50° C.=45° C.=ΔT_(spec). Thus,45° C. defines, in this example, the critical limit temperature(T_(max,crit)).

Assuming that the difference between the hot temperature and the ambienttemperature (T_(hot)−T_(amb)) readings does not exceed the maximumcritical temperature difference indicative of a low airflow, processingdetermines whether the temperature difference between the hot andambient temperature (T_(hot)−T_(amb)) readings exceeds a low airflowwarning limit temperature (T_(max,warn)), which corresponds to atemperature indicative of an airflow across the airflow sensor which isat or below the minimum airflow desired for the electronic system to beadequately cooled. In one example, this warning temperature threshold(T_(max,warn)) might be 50° C. If the above-noted critical temperaturethreshold (T_(max,crit)) is breached, an error message is sent and theelectronic system is deactivated 650. However, if the warningtemperature threshold (T_(max,warn)) is exceeded, then an error messageis posted 660, but operation continues, and if no temperature thresholdsare exceeded, then processing continues to cycle through the monitoringloop.

As described herein, the airflow sensor employed within the monitoringprocess is initially calibrated for the particular electronic system. Inparticular, depicted in FIGS. 7A & 7B is one approach to calibrating theduty cycle for powering the heater of the airflow sensor to ensure thatthe sensor does not indicate a low airflow when sufficient airflowexists, and to ensure that the airflow sensor indicates low airflow whenthe system/enclosure is at risk of overheating.

Referring initially to FIG. 7A, airflow sensor calibration begins withascertaining a known ambient temperature and a desired ambient airflowrate across the electronic system 700. A first duty cycle n₁, and asecond duty cycle n₂ are chosen or set, and an acceptable temperaturedifferential (ΔT_(spec)) is specified 705. The indexes i and j areinitialized to 1 710, and the airflow sensor heater(s) is cycled usingduty cycle n_(j) 715. Processing waits a time interval t 720 for thetemperature to stabilize, and reads (in one embodiment) the airflowsensor's first temperature sensor (T_(hot)), and second temperaturesensor (T_(amb)), and calculates a temperature difference between thehot sensor and ambient temperatures (T_(hot)−T_(amb)), which is storedas ΔT_(j,i) 725. Next, “1” is added to index i 730, and a determinationis made whether two or more temperature differences have been determinedfor the current duty cycle n_(j) 735. If “no”, then processing returnsto wait time interval t 720 and repeat the process.

Once at least two temperature differences have been calculated,processing determines whether the time rate of change for the last twotemperature readings (ΔT_(j,i-1), ΔT_(j,i-2)) is less than a set steadystate criteria 740. By way of example, the set steady state criteriamight be 0.1° C./min. If “no”, then processing returns to determine anext temperature difference between the hot temperature reading andambient temperature reading (T_(hot)−T_(amb)). If “yes”, then the timerate of change is recorded (ΔT_(j)) for duty cycle n_(j), and “1” isadded to index j 745. Processing determines whether j is greater thantwo 750, and if “no”, returns to cycle the airflow sensor heater usingduty cycle n_(j) to obtain another time rate of change reading (ΔT_(j))for another duty cycle n_(j).

Referring to FIG. 7B, once j is greater than two, then processingcompares the current temperature difference (ΔT_(j)) to the specifiedtemperature difference (ΔT_(spec)) plus or minus a tolerance (ε) band755. If “no”, then a duty cycle is calculated to achieve the specifiedtemperature difference (ΔT_(spec)) 760, and the calculated duty cycle issaved as duty cycle n_(j) 765, after which processing returns to cyclethe airflow sensor heater using duty cycle n_(j) to obtain another timerate of change reading (ΔT_(j)) for duty cycle n_(j). Note that dutycycle n_(j) can be calculated using:

$n_{j} = {\frac{\left( {{\Delta \; T_{spec}} - {\Delta \; T_{j - 1}}} \right)\left( {n_{j - 1} - n_{j - 2}} \right)}{{\Delta \; T_{j - 1}} - {\Delta \; T_{j - 2}}} + n_{j - 1}}$

If the current temperature difference (ΔT_(j)) is within the specifiedtemperature difference (ΔT_(spec)) plus or minus the tolerance band 755,then processing saves to non-volatile memory the current duty cycle asachieving the specified temperature reading tolerance at the givenambient temperature and airflow rate 770, which completes calibration ofthe airflow sensor 775.

Those skilled in the art will note from the above description thatdisclosed herein is, in one aspect, a method of calibrating an airflowsensor within an electronic system/enclosure. In one embodiment, theairflow sensor includes one or more temperature sensors, one of whichhas associated therewith a varying power duty cycle such that theairflow rate through the electronic system can be inferred, and comparedto one or more threshold values. Based on the comparison, speed of oneor more air moving devices associated with the electronic system may beadjusted or power to the electronic system may be deactivated. Asdescribed herein, calibrating the duty cycle may include calculating ameasured hot to ambient temperature difference for a first and secondduty cycle, determining subsequent duty cycles using the measurements ofthe previous two duty cycles, converging upon a duty cycle which at aknown airflow produces a desired temperature difference. The derivedduty cycle is then saved to nonvolatile memory, for example, within theassociated electronic system/enclosure, and subsequently used inoperation of the airflow sensor so that despite differences betweenairflow sensors, low airflow and high ambient conditions can beidentified without “fault trips”.

As will be appreciated by one skilled in the art, control and/orcalibration aspects of the present invention may be embodied as asystem, method or computer program product. Accordingly, aspects of thepresent invention may take the form of an entirely hardware embodiment,an entirely software embodiment (including firmware, resident software,micro-code, etc.) or an embodiment combining software and hardwareaspects that may all generally be referred to herein as a “circuit,”“module” or “system”. Furthermore, control and/or calibration aspects ofthe present invention may take the form of a computer program productembodied in one or more computer readable medium(s) having computerreadable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readable signalmedium may be any non-transitory computer readable medium that is not acomputer readable storage medium and that can communicate, propagate, ortransport a program for use by or in connection with an instructionexecution system, apparatus or device.

A computer readable storage medium may be, for example, but not limitedto, an electronic, magnetic, optical, electromagnetic, infrared orsemiconductor system, apparatus, or device, or any suitable combinationof the foregoing. More specific examples (a non-exhaustive list) of thecomputer readable storage medium include the following: an electricalconnection having one or more wires, a portable computer diskette, ahard disk, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), anoptical fiber, a portable compact disc read-only memory (CD-ROM), anoptical storage device, a magnetic storage device, or any suitablecombination of the foregoing. In the context of this document, acomputer readable storage medium may be any tangible medium that cancontain or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

Referring now to FIG. 8, in one example, a computer program product 800includes, for instance, one or more computer readable storage media 802to store computer readable program code means or logic 804 thereon toprovide and facilitate one or more aspects of the present invention.

Program code embodied on a computer readable medium may be transmittedusing an appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out control and/or calibrationoperations for aspects of the present invention may be written in anycombination of one or more programming languages, including an objectoriented programming language, such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language, assembler or similar programming languages. Theprogram code may execute entirely on the user's computer, partly on theuser's computer, as a stand-alone software package, partly on the user'scomputer and partly on a remote computer or entirely on the remotecomputer or server. In the latter scenario, the remote computer may beconnected to the user's computer through any type of network, includinga local area network (LAN) or a wide area network (WAN), or theconnection may be made to an external computer (for example, through theInternet using an Internet Service Provider).

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

In addition to the above, one or more aspects of the present inventionmay be provided, offered, deployed, managed, serviced, etc. by a serviceprovider who offers management of customer environments. For instance,the service provider can create, maintain, support, etc. computer codeand/or a computer infrastructure that performs one or more aspects ofthe present invention for one or more customers. In return, the serviceprovider may receive payment from the customer under a subscriptionand/or fee agreement, as examples. Additionally or alternatively, theservice provider may receive payment from the sale of advertisingcontent to one or more third parties.

In one aspect of the present invention, an application may be deployedfor performing one or more aspects of the present invention. As oneexample, the deploying of an application comprises providing computerinfrastructure operable to perform one or more aspects of the presentinvention.

As a further aspect of the present invention, a computing infrastructuremay be deployed comprising integrating computer readable code into acomputing system, in which the code in combination with the computingsystem is capable of performing one or more aspects of the presentinvention.

As yet a further aspect of the present invention, a process forintegrating computing infrastructure comprising integrating computerreadable code into a computer system may be provided. The computersystem comprises a computer readable medium, in which the computermedium comprises one or more aspects of the present invention. The codein combination with the computer system is capable of performing one ormore aspects of the present invention.

Although various embodiments are described above, these are onlyexamples. For example, computing environments of other architectures canincorporate and use one or more aspects of the present invention.Additionally, the network of nodes can include additional nodes, and thenodes can be the same or different from those described herein. Also,many types of communications interfaces may be used.

Further, a data processing system suitable for storing and/or executingprogram code is usable that includes at least one processor coupleddirectly or indirectly to memory elements through a system bus. Thememory elements include, for instance, local memory employed duringactual execution of the program code, bulk storage, and cache memorywhich provide temporary storage of at least some program code in orderto reduce the number of times code must be retrieved from bulk storageduring execution.

Input/Output or I/O devices (including, but not limited to, keyboards,displays, pointing devices, DASD, tape, CDs, DVDs, thumb drives andother memory media, etc.) can be coupled to the system either directlyor through intervening I/O controllers. Network adapters may also becoupled to the system to enable the data processing system to becomecoupled to other data processing systems or remote printers or storagedevices through intervening private or public networks. Modems, cablemodems, and Ethernet cards are just a few of the available types ofnetwork adapters.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include” (and any formof include, such as “includes” and “including”), and “contain” (and anyform contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises”, “has”,“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of a method or anelement of a device that “comprises”, “has”, “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention throughvarious embodiments and the various modifications thereto which aredependent on the particular use contemplated.

1-15. (canceled)
 16. A monitored electronic system comprising: anelectronic system at least partially air-cooled; and a monitoring devicefor monitoring air-cooling of the electronic system, the monitoringdevice comprising: an airflow sensor positioned within the electronicsystem, the airflow sensor comprising at least one temperature sensorand a heater associated with one temperature sensor of the at least onetemperature sensor; non-volatile memory containing a calibrated dutycycle for use in powering the heater associated with the one temperaturesensor of the at least one temperature sensor, the calibrated duty cyclehaving been obtained with the airflow sensor positioned within theelectronic system; and a controller, the controller being configured touse the calibrated duty cycle in powering the heater associated with theone temperature sensor of the at least one temperature sensor duringairflow monitoring of the electronic system, and to obtain a hottemperature (T_(hot)) reading from the one temperature sensor having theassociated heater powered using the calibrated duty cycle, and todetermine, based at least in part on the hot temperature (T_(hot))reading, whether to issue a warning.
 17. The monitored electronic systemof claim 16, wherein the airflow sensor is positioned on an electronicboard within the electronic system, and the controller is configured todetermine whether the hot temperature (T_(hot)) reading is above amaximum acceptable board temperature (T_(max,b)), and responsive to thehot temperature (T_(hot)) reading being above the maximum acceptableboard temperature (T_(max,b)), to issue a critical electronic board overtemperature warning as the warning, and deactivate the electronicsystem.
 18. The monitored electronic system of claim 16, wherein thecontroller is further configured to obtain an ambient temperature(T_(amb)) reading from the at least one temperature sensor to determinewhether a difference between the hot temperature (T_(hot)) reading andthe ambient temperature (T_(amb)) reading is above a criticaltemperature difference threshold (T_(max,crit)), and responsive to thedifference between the hot temperature (T_(hot)) reading and the ambienttemperature (T_(amb)) reading exceeding the critical hot temperaturethreshold (T_(max,crit)), to issue a critical airflow indication as thewarning and to deactivate the electronic system.
 19. The monitoredelectronic system of claim 16, wherein the controller is furtherconfigured to obtain an ambient temperature (T_(amb)) reading from theat least one temperature sensor, and to determine whether a differencebetween the hot temperature (T_(hot)) reading and the ambienttemperature (T_(amb)) reading exceeds a warning temperature differencethreshold (T_(max,warn)), and responsive to the difference between thehot temperature (T_(hot)) reading and the ambient temperature (T_(amb))reading exceeding the warning temperature difference threshold(T_(max,warn)), to automatically issue an airflow warning indication asthe warning.
 20. The monitored electronic system of claim 16, whereincalibrating the duty cycle comprises: (i) initiating airflow sensorcalibration employing a known ambient temperature and a known ambientairflow rate across the electronic system; (ii) setting a first dutycycle n₁, a second duty cycle n₂, and an acceptable, specifiedtemperature differential (ΔT_(spec)); (iii) initializing an index i andan index j to 1; (iv) cycling powering of the heater using duty cyclen_(j); (v) reading the one temperature sensor with the associated heaterto obtain a hot temperature (T_(hot)) reading, and obtaining an ambienttemperature (T_(amb)) reading from the at least one temperature sensor,and calculating a temperature difference between the hot temperature(T_(hot)) reading and the ambient temperature (T_(amb)) reading, andsaving the temperature difference as ΔT_(j,i); (vi) adding 1 to index i;(vii) determining whether the time rate of change over the last twotemperature difference readings (ΔT_(j,i-1), ΔT_(j,i-2)) is less than aset steady state criteria, and responsive to the time rate of changeover the last two temperature difference readings not being below theset steady state criteria, returning to obtain another hot temperature(T_(hot)) reading and another ambient temperature (T_(amb)) reading,otherwise, recording the temperature difference (ΔT_(j)), and add 1 toindex j; viii) determining whether the current temperature difference(ΔT_(j)) is at the specified temperature difference (ΔT_(spec)) plus orminus a tolerance band; and (ix) responsive to the determinedtemperature difference (ΔT_(j)) being at the specified temperaturedifference (ΔT_(spec)) plus or minus the tolerance band, saving thecurrent duty cycle n_(j) as the calibrated duty cycle, the calibratedduty cycle facilitating obtaining the acceptable, specified temperaturedifference.